Improved Nitrogen Management for an Intensive Winter Wheat/Summer Maize Double-cropping System

Improving N and straw management to achieve high crop yields, minimize nitrate leaching, and balance soil fertility presents challenges in winter wheat (Triticum aestivum L.)/summer maize (Zea mays L.) double cropping systems on the North China Plain. A long-term field experiment was designed to study crop performance, nitrate leaching, and N balance under three N management approaches (conventional farming practice, improved N-min, and N balance methods) with two straw management options (straw removal and return), and two types of organic amendment (cattle [Bos taurus] manure and municipal waste compost). Grain and straw yields and C/N ratios were determined in each crop, together with N uptake and residual NO3-N in the top 2 m of the soil profile. Over six successive crops of the study (October 2006-September 2009) 32 to 93% of applied N was saved without reducing either wheat or maize yields and less NO3-N accumulated in the top 1 m of the soil (the root zone) or leached 1 to 2 m down the soil profile when the two new N management approaches were used in comparison with conventional N management. Straw return did not affect crop yield or NO3-N accumulation but the N rate with straw return in the improved N-min method increased due to N immobilization induced by the straw. Moreover, in the hot and wet maize seasons, chemical fertilizer N rate in the N balance method can further decrease by reducing the target residual NO3-N in the 0 to 1 m root zone and by increasing the percentage availability of total N in organic amendments in future studies.